Current techniques for evaluating human male fertility are imprecise. Penetration of zona-free hamster ova by human sperm has been suggested as an in vitro assay for fertility of human sperm. However, significant variability exists among the few published preliminary reports in methodology and in penetration percentages by fertile sperm. The first aim of this research is to define optimal conditions for this assay. The sensitivity of the assay to variations in both treatment of ova and treatment of sperm will be determined. The second aim is to examine a large population of apparently fertile and apparently infertile males to test the merit of the assay under the determined conditions. This will establish the range of penetration values expected for sperm from fertile and subfertile to infertile males. The third aim of this research is to test whether sperm penetrating ability is highly correlated with the sperm's ability to undergo the ionophore A23187-induced acrosome reaction. Release of hyaluronidase will be used to quantify the occurrence of the acrosome reaction. The fourth aim is to begin studies on possible differences in surface proteins between fertile and infertile samples. These will be compared before and after incubation in capacitating conditions. Initial examination of surface proteins will be by iodination followed by gel electrophoresis and isoelectric focusing. The results of this research should contribute to an improved technique for assessing male fertility in vitro and to the understanding and eventual treatment of infertility.